1. Field of the Invention
The present invention relates to a polymeric colorant suitably used for coloring ocular lenses such as a contact lens, an intraocular lens and an artificial cornea, and a colored material for forming the ocular lenses, which uses the polymeric colorant.
2. Discussion of the Related Art
There have been proposed various polymeric colorants for coloring a composition or material which is used for forming a colored product. In the field of manufacture of an ocular lens such as a contact lens or an intraocular lens, for instance, a lens composition or material (lens-forming composition) used for producing the ocular lens is copolymerized with a suitable polymeric colorant, to thereby provide a colored material from which the intended ocular lens is produced. The ocular lens formed of such a colored material is uniformly colored and exhibits a high degree of resistance to exposure to light and chemical substances without suffering from decoloring or a change in its color, which would be caused by separation or elution of the colorant from the colored material.
JP-A-1-280464 discloses, as one example of the polymeric colorant for coloring the ocular lens, a polymeric colorant of azo-system or an azo-derived polymeric colorant wherein one of acryloyloxy, methacryloyloxy, vinyl, and aryl groups is substituted for at least one hydrogen atom of a naphthyl group which is bonded to an azo group. This polymeric colorant of the azo system is copolymerized with a vinyl monomer, to thereby provide a vinyl polymer from which the intended colored lens is produced.
JP-A-1-299560 discloses a colored ocular lens material obtained by copolymerizing a suitably selected copolymerizable lens-forming monomer component, a polymeric UV absorbent including a suitable polymeric group, and a polymeric colorant including a polymeric group which is selected from the group consisting of an acryloyl group, a methacryloyl group, a vinyl group, an aryl group, and an isopropenyl group. This colored ocular lens material does not suffer from elution of the UV absorbent and the colorant, and exhibits excellent durability. The colorant used in this ocular lens material is a polymeric colorant of azo system, wherein the polymeric group suitably selected from among those described above is introduced into a phenyl group or a naphthyl group bonded to the azo group, via an ester bond or an amide bond.
JP-A-8-503997 discloses a polymerizable yellow dye of azo system, wherein an unsaturated organic group having an ester structure or an amide structure is introduced into a phenyl group bonded to the azo group, via nitrogen or alkyl. This polymerizable yellow dye is polymerized with a lens-forming monomer component such as acrylate monomer or methacrylate monomer, to thereby provide a colored ocular lens material.
In those polymeric colorants described above wherein the polymeric unsaturated group is introduced via an oxygen atom into the aromatic ring in the phenyl or naphthyl group bonded to the azo group, the unsaturated group is bonded or attached to the aromatic ring by the ester bond formed therebetween. The polymeric colorant in which the ester bond is directly attached to the aromatic ring as described above tends to suffer from easy hydrolysis, whereby the colorant is chemically unstable, making its handling difficult. Further, the original color tone of the colorant undesirably changes due to the introduction of the polymeric group. In this case, it is difficult to predict the color tone of the colorant in the end product.